Don't loop infinitely long on serial comm failures

If serial uart (8250/16x50) takes abnormally long to respond, give
up on logging to serial console and instead let the system boot.

Also reference bit in LSR register with correct name.

Change-Id: I3796efc3e8690425f04a130af4bc99541b64d335
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/611
Tested-by: build bot (Jenkins)
Reviewed-by: Peter Stuge <peter@stuge.se>

diff --git a/src/lib/uart8250.c b/src/lib/uart8250.c
index b2246713cac087d03d4f010121219ace09eff13b..fe8ed705d651341f1a6806a3e959358d3aa39115 100644 (file)
--- a/src/lib/uart8250.c
+++ b/src/lib/uart8250.c
@@ -29,21 +29,30 @@
 
 /* Should support 8250, 16450, 16550, 16550A type UARTs */
 
+/* Expected character delay at 1200bps is 9ms for a working UART
+ * and no flow-control. Assume UART as stuck if shift register
+ * or FIFO takes more than 50ms per character to appear empty.
+ *
+ * Estimated that inb() from UART takes 1 microsecond.
+ */
+#define SINGLE_CHAR_TIMEOUT    (50 * 1000)
+#define FIFO_TIMEOUT           (16 * SINGLE_CHAR_TIMEOUT)
+
 static inline int uart8250_can_tx_byte(unsigned base_port)
 {
-       return inb(base_port + UART_LSR) & UART_MSR_DSR;
+       return inb(base_port + UART_LSR) & UART_LSR_THRE;
 }
 
 static inline void uart8250_wait_to_tx_byte(unsigned base_port)
 {
-       while(!uart8250_can_tx_byte(base_port))
-               ;
+       unsigned long int i = SINGLE_CHAR_TIMEOUT;
+       while (i-- && !uart8250_can_tx_byte(base_port));
 }
 
 static inline void uart8250_wait_until_sent(unsigned base_port)
 {
-       while(!(inb(base_port + UART_LSR) & UART_LSR_TEMT))
-               ;
+       unsigned long int i = FIFO_TIMEOUT;
+       while (i-- && !(inb(base_port + UART_LSR) & UART_LSR_TEMT));
 }
 
 void uart8250_tx_byte(unsigned base_port, unsigned char data)
@@ -64,9 +73,13 @@ int uart8250_can_rx_byte(unsigned base_port)
 
 unsigned char uart8250_rx_byte(unsigned base_port)
 {
-       while(!uart8250_can_rx_byte(base_port))
-               ;
-       return inb(base_port + UART_RBR);
+       unsigned long int i = SINGLE_CHAR_TIMEOUT;
+       while (i-- && !uart8250_can_rx_byte(base_port));
+       
+       if (i)
+               return inb(base_port + UART_RBR);
+       else
+               return 0x0;
 }
 
 void uart8250_init(unsigned base_port, unsigned divisor)
@@ -83,7 +96,7 @@ void uart8250_init(unsigned base_port, unsigned divisor)
        /* DLAB on */
        outb(UART_LCR_DLAB | CONFIG_TTYS0_LCS, base_port + UART_LCR);
 
-       /* Set Baud Rate Divisor. 12 ==> 115200 Baud */
+       /* Set Baud Rate Divisor. 12 ==> 9600 Baud */
        outb(divisor & 0xFF,   base_port + UART_DLL);
        outb((divisor >> 8) & 0xFF,    base_port + UART_DLM);